Transmission Range Switch Circuit Diagnosis

Circuit Description
The transmission on this vehicle has a Park Neutral Position (PNP) and Back-up switch. This switch incorporates a transmission range selector switch. There are four inputs (PRND A, B, C, P) which are switches to ground. The four switches have an unique switch pattern. The PCM uses the combination of the switch patterns in order to determine the gear selected by the driver.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

The following may cause an intermittent:
^ Inspect for poor connections. Refer to Intermittents and Poor Connections Diagnosis.
^ Corrosion.
^ Mis-routed harness.
^ Rubbed through wire insulation.
^ Broken wire inside the insulation.
^ Manipulate related wiring and connectors while observing the PRND Range parameters (PRND A, B, C, P) on the scan tool. If the manipulation causes an intermittent, the corresponding parameter changes on the scan tool.
^ The table is the normal state that each gear range should indicate. ON indicates the circuit is low (switched/shorted to a ground). OFF indicates the circuit is high (open). Another parameter to display is PRND Range. This parameter displays the current gear range the transmission is in. When there is an invalid gear range, the parameter indicates Invalid.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This verifies whether a malfunction is present. If the PCM does not detect any invalid ranges, this indicates the fault is not present. You may have repaired the fault when the switch was adjusted.
4. Any circuit that you suspect is causing an intermittent condition, thoroughly inspect for the following:
^ Backed out terminals
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Poor terminal to wiring connections
^ Physical damage to the wiring harness
5. A circuit malfunction causes the Trans Range to display an invalid range on the scan tool. Jumping each circuit to ground simulates the trans range switch operation and tests the circuitry and PCM. While the transmission range switch is disconnected and the circuits are not grounded, the scan tool should indicate OFF. A value that indicates ON with no jumper to ground indicates a grounded circuit or malfunctioning PCM. Intermittent Conditions